This phase-II study is designed to explore relevant scientific questions while examining new treatment options for ACTG 320 enrollees (and a limited number of non-ACTG 320 volunteers, if needed) who have been receiving ZDV (or d4T) + 3TC + indinavir and are currently exhibiting a range of virologic responses. By dividing the study into the corresponding, non-sequential cohorts (Groups A, B, C and D), different approaches to evaluating virologic success (i.e., undetectable plasma HIV-1 RNA levels) and virologic failure (i.e., plasma HIV-1 RNA levels 3500 copies/ml) can be explored while maintaining long-term follow-up of ACTG 320 subjects. Providing rollover options for all subjects on a particular regimen in an ACTG trial, irrespective of response, is a desirable goal as new approaches to managing response and failure can be pursued in parallel and in an efficient manner.